This invention is directed to a speed control system for hydrostatic drives and particularly to speed control systems that have insufficient engine braking power to provide braking to the system or limit the amount of engine over-speed.
Systems for controlling speed and in hydrostatic drives with insufficient braking power are known in the art. As an example, an integrated speed limiter (ISL) consists of a pilot pressure setting and bypass orifice acting with a pressure reducing valve to automatically limit the pump torque input to the engine. Excess hydrostatic power is converted to heat. In these systems, the pressure reduction of oil occurs inline between the pump and motor rotating kits. Oil passes through the pressure reducing valve and into the pump rotating kit. Examples include U.S. Pat. Nos. 7,201,183; 7,121,297; 6,360,537; 6,338,247 and 5,121,603.
Similarly, systems which function based on an operator brake input device with microcontroller for systems with insufficient engine braking power are known in the art. For example, U.S. Pat. No. 7,874,153 teaches a system where motors swivel out proportionally to brake pedal travel and braking takes place by means of diesel engine drag torque with secondary force applied via pressure relief valves. In this system, the flow path of the pressure reduction is different than the previous example (i.e., ISL). The pressure relief consumes a portion of the flow being transmitted from the motor. This flow bypasses the pump rotating kit to the low pressure side of the circuit.
While helpful, these systems do not address the need for a system which functions automatically (with or without operator input) and is controlled and configured by a microcontroller. Needed is a system with maximum and immediate utilization of available drag torque possible when demanded, with or without operator input from a control lever, brake input device, or some other physical device. Also needed is a system which can automatically transition to a condition where vehicle braking can exceed the engine's capability.
An objective of the present invention is to provide a speed control system for a hydrostatic transmission that automatically adjusts speed through use of a microcontroller.
Another objective of the present invention is to provide a speed control system for a hydrostatic transmission that immediately maximizes the use of available drag torque when demanded and can provide immediate braking beyond the capability of the engine with no delay.
These and other objectives will be apparent to one of ordinary skill in the art based upon the following written description, drawings and claims.